Muthukumaran Packirisamy

Planar waveguide echelle gratings in silica-on-silicon

Silica planar waveguide echelle grating demultiplexers with 48 channels and 256 channels are described and demonstrated. Polarization effects due to stress birefringence and polarization-dependent grating efficiency have been eliminated using a modified polarization compensator and grating design. The devices have a polarization-dependent wavelength shift of less than 10 pm, and a polarization-dependent loss below 0.2 dB. The 48-channel device has a measured crosstalk of -35 dB, an insertion loss better than 4 dB, and a uniformity of 1 dB across the C-band.

A multifunctional PVDF-based tactile sensor for minimally invasive surgery

In this paper a multifunctional tactile sensor system using PVDF (polyvinylidene fluoride), is proposed, designed, analyzed, tested and validated. The working principle of the sensor is in such a way that it can be used in combination with almost any end-effectors. However, the sensor is particularly designed to be integrated with minimally invasive surgery (MIS) tools. In addition, the structural and transduction materials are selected to be compatible with micro-electro-mechanical systems (MEMS) technology, so that miniaturization would be possible. The corrugated shape of the sensor ensures the safe tissue grasping and compatibility with the traditional tooth-like end effectors of MIS tools. A unit of this sensor comprised of a base, a flexible beam and three PVDF sensing elements. Two PVDF sensing elements sandwiched at the end supports work in thickness mode to measure the magnitude and position of applied load. The third PVDF sensing element is attached to the beam and it works in the extensional mode to measure the softness of the contact object. The proposed sensor is modeled both analytically and numerically and a series of simulations are performed in order to estimate the characteristics of the sensor in measuring the magnitude and position of a point load, distributed load, and also the softness of the contact object. Furthermore, in order to validate the theoretical results, the prototyped sensor was tested and the results are compared. The results are very promising and proving the capability of the sensor for haptic sensing.

Quantitative Boundary Support Characterization for Cantilever MEMS

Microfabrication limitations are of concern especially for suspended Micro-Electro-Mechanical-Systems (MEMS) microstructures such as cantilevers. The static and dynamic qualities of such microscale devices are directly related to the invariant and variant properties of the microsystem. Among the invariant properties, microfabrication limitations can be quantified only after the fabrication of the device through testing. However, MEMS are batch fabricated in large numbers where individual testing is neither possible nor cost effective. Hence, a suitable test algorithm needs to be developed where the test results obtained for a few devices can be applied to the whole fabrication batch, and also to the foundry process in general. In this regard, this paper proposes a method to test MEMS cantilevers under variant electro-thermal influences in order to quantify the effective boundary support condition obtained for a foundry process. A non-contact optical sensing approach is employed for the dynamic testing. The Rayleigh-Ritz energy method using boundary characteristic orthogonal polynomials is employed for the modeling and theoretical analysis.

Modelling and control of an electrostatically actuated torsional micromirror

This work aims at developing control algorithms for an electrostatically actuated torsional micromirror, extending the operational range of the device to a full 90° tilt angle. The analytical model of the micromirror equipped with an additional vertical electrode is established. Since the geometrical extent of the device is comparable to the air gap, the effect of the fringing field is also incorporated into the model. It is shown that the considered system is differentially flat and, based on this property, a closed-loop control scheme is constructed for both scanning control and set-point control. In addition, the desired performance can be specified through reference trajectories, allowing the control system tuning to be performed in a systematic way. The simulation results demonstrate the advantage of the developed control scheme over the constant voltage control.

A polyimide based resistive humidity sensor

Purpose – To establish an accurate and sensitive method to characterize the moisture content of a particular environment.Design/methodology/approach – This paper proposes a relatively simple humidity sensor design consisting of electrodes on a suitable substrate coated with a polyimide material. The changes in relative humidity are denoted by a corresponding change in the polyimide materials electrical resistance profile. The design proposed in this work can be microfabricated and integrated with electronic circuitry. This sensor can be fabricated on alumina or silicon substrates. The electrode material can be made up of nickel, gold or aluminum and the thickness of the electrodes ranges typically between 0.2 and 0.3 μm. The sensor consists of an active sensing layer on top of a set of electrodes. The design of the electrodes can be configured for both resistive and capacitive sensing.Findings – The polyimide materials ohmic resistance changes significantly with humidity variations. Changes in resistanc...

An improved method for predicting microfabrication influence in atomic force microscopy performances

This paper presents the application of the concept of boundary conditioning to the prediction of spring constant of atomic force microscope (AFM) cantilevers after considering the inherent microfabrication limitations. The boundary support conditions of micromechanical structures such as AFM probes are non-classical in nature, and they influence the modal response and natural frequencies of the cantilever that cannot be modelled on purely classical boundary conditions. In this paper, an AFM cantilever end support is modelled with artificial translational and rotational springs in order to capture the deviation from classical boundary conditions. The dynamic and static behaviour of the beam is investigated by the Rayleigh-Ritz energy method using boundary characteristic orthogonal polynomials and compared with published theoretical and experimental results. The comparison shows a close agreement and presents an insight into the inherent limitation associated with AFM probe fabrication processes that would affect the stiffness of the probe.

Boundary characterization of microstructures through thermo-mechanical testing

A variety of silicon foundry processes available for microsystem implementation are available at the present time. The manufacturing methods and the associated process tolerances employed at a particular foundry will determine the performance of the finished devices. Moreover, micro-electro-mechanical systems (MEMS) often require processes that are difficult to control. Device-to-device variations can occur even in batch microfabricated systems. One particular limitation of MEMS foundry processes, in general, is associated with non-classical boundary support conditions due to over/under etching of silicon. These non-classical support conditions will affect the static and dynamic performance of the microsystem. This condition has important implications in atomic force microscopy applications where the targeted natural frequencies are given a wide tolerance due in large part to microfabrication limitations. This paper presents the boundary characterization of single crystal silicon microcantilevers through thermo-mechanical testing. A non-contact optical sensing approach is used for the experimentation. The Rayleigh–Ritz energy method incorporating boundary characteristic orthogonal polynomials is used for the prediction analysis.

Tuning the dynamic behaviour of cantilever MEMS based sensors and actuators

Purpose – This paper seeks to establish an analytical reference model in order to optimize the frequency response of MEMS cantilever structures using cutouts.Design/methodology/approach – Presented in this work is a method to tune the frequency response of MEMS cantilevers by using single cutouts of various sizes. From an interpretation of the analytical results, mass and stiffness domains are defined as a function of the cutout position on the cantilever. In this regard, the elastic properties of the MEMS cantilever can be trimmed through mechanical tuning by a single cutout incorporated into the device geometry. The Rayleigh‐Ritz energy method is used for the modeling. Analytical results are compared with FEM and experimental results.Findings – The eigenvalues are dependent on the position and size of the cutout. Hence, the frequency response of the cantilever can be tuned and optimized through this approach.Research limitations/implications – MEMS microsystems are sensitive to microfabrication limitati...

Hybrid Integrated Silicon Microfluidic Platform for Fluorescence Based Biodetection

The desideratum to develop a fully integrated Lab-on-a-chip device capable of rapid specimen detection for high throughput in-situ biomedical diagnoses and Point-of-Care testing applications has called for the integration of some of the novel technologies such as the microfluidics, microphotonics, immunoproteomics and Micro Electro Mechanical Systems (MEMS). In the present work, a silicon based microfluidic device has been developed for carrying out fluorescence based immunoassay. By hybrid attachment of the microfluidic device with a Spectrometer-on-chip, the feasibility of synthesizing an integrated Lab-on-a-chip type device for fluorescence based biosensing has been demonstrated. Biodetection using the microfluidic device has been carried out using antigen sheep IgG and Alexafluor-647 tagged antibody particles and the experimental results prove that silicon is a compatible material for the present application given the various advantages it offers such as cost-effectiveness, ease of bulk microfabrication, superior surface affinity to biomolecules, ease of disposability of the device etc., and is thus suitable for fabricating Lab-on-a-chip type devices.

Graphical Rendering of Localized Lumps for MIS Applications

Minimally invasive sugery (MIS) has increasingly been used in different surgical routines despite having significant shortcomings such as a lack of tactile feedback. Restoring this missing tactile information, particularly the information gained through tissue palpation, would be a significant enhancement to MIS capabilities. Tissue palpation is particularly important and commonly used in locating embedded lumps. The present study is inspired by this major limitation of the MIS procedure and is aimed at developing a system to reconstruct the lost palpation capability of surgeons in an effective way. By collecting necessary information on the size and location of hidden features using MIS graspers equipped with tactile sensors, the information can be processed and graphically rendered to the surgeon. Therefore, using the proposed system, surgeons can identify the presence or absence, location, and approximate size of hidden lumps simply by grasping the target organ with a smart endoscopic grasper. The results of the conducted experiments on the prototyped MIS graspers represented by graphical images are compared with those of the finite element models.